drm/i915/display: Add Nearest-neighbor based integer scaling support

Integer scaling (IS) is a nearest-neighbor upscaling technique that
simply scales up the existing pixels by an integer
(i.e., whole number) multiplier.Nearest-neighbor (NN) interpolation
works by filling in the missing color values in the upscaled image
with that of the coordinate-mapped nearest source pixel value.

Both IS and NN preserve the clarity of the original image. Integer
scaling is particularly useful for pixel art games that rely on
sharp, blocky images to deliver their distinctive look.

Introduce functions to configure the scaler filter coefficients to
enable nearest-neighbor filtering.

Bspec: 49247

changes since v6:
* Trust compiler, remove pointless inline keyword from cnl_coef_tap()
  & cnl_nearest_filter_coef() functions (Ville)
changes since v4:
* Make cnl_coef_tap(), cnl_nearest_filter_coef() inline (Uma)
changes since v3:
* None
changes since v2:
* Move APIs from 5/5 into this patch.
* Change filter programming related function names to cnl_*, move
  filter select bits related code into inline function (Ville)
changes since v1:
* Rearrange skl_scaler_setup_nearest_neighbor_filter() to iterate the
  registers directly instead of the phases and taps (Ville)

changes since RFC:
* Refine the skl_scaler_setup_nearest_neighbor_filter() logic (Ville)
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201020161427.6941-4-pankaj.laxminarayan.bharadiya@intel.com

drivers/gpu/drm/i915/display/intel_display.c

@@ -6289,6 +6289,105 @@ void skl_scaler_disable(const struct intel_crtc_state *old_crtc_state)
 		skl_detach_scaler(crtc, i);
 }
 
+static int cnl_coef_tap(int i)
+{
+	return i % 7;
+}
+
+static u16 cnl_nearest_filter_coef(int t)
+{
+	return t == 3 ? 0x0800 : 0x3000;
+}
+
+/**
+ *  Theory behind setting nearest-neighbor integer scaling:
+ *
+ *  17 phase of 7 taps requires 119 coefficients in 60 dwords per set.
+ *  The letter represents the filter tap (D is the center tap) and the number
+ *  represents the coefficient set for a phase (0-16).
+ *
+ *         +------------+------------------------+------------------------+
+ *         |Index value | Data value coeffient 1 | Data value coeffient 2 |
+ *         +------------+------------------------+------------------------+
+ *         |   00h      |          B0            |          A0            |
+ *         +------------+------------------------+------------------------+
+ *         |   01h      |          D0            |          C0            |
+ *         +------------+------------------------+------------------------+
+ *         |   02h      |          F0            |          E0            |
+ *         +------------+------------------------+------------------------+
+ *         |   03h      |          A1            |          G0            |
+ *         +------------+------------------------+------------------------+
+ *         |   04h      |          C1            |          B1            |
+ *         +------------+------------------------+------------------------+
+ *         |   ...      |          ...           |          ...           |
+ *         +------------+------------------------+------------------------+
+ *         |   38h      |          B16           |          A16           |
+ *         +------------+------------------------+------------------------+
+ *         |   39h      |          D16           |          C16           |
+ *         +------------+------------------------+------------------------+
+ *         |   3Ah      |          F16           |          C16           |
+ *         +------------+------------------------+------------------------+
+ *         |   3Bh      |        Reserved        |          G16           |
+ *         +------------+------------------------+------------------------+
+ *
+ *  To enable nearest-neighbor scaling:  program scaler coefficents with
+ *  the center tap (Dxx) values set to 1 and all other values set to 0 as per
+ *  SCALER_COEFFICIENT_FORMAT
+ *
+ */
+
+static void cnl_program_nearest_filter_coefs(struct drm_i915_private *dev_priv,
+					     enum pipe pipe, int id, int set)
+{
+	int i;
+
+	intel_de_write_fw(dev_priv, CNL_PS_COEF_INDEX_SET(pipe, id, set),
+			  PS_COEE_INDEX_AUTO_INC);
+
+	for (i = 0; i < 17 * 7; i += 2) {
+		u32 tmp;
+		int t;
+
+		t = cnl_coef_tap(i);
+		tmp = cnl_nearest_filter_coef(t);
+
+		t = cnl_coef_tap(i + 1);
+		tmp |= cnl_nearest_filter_coef(t) << 16;
+
+		intel_de_write_fw(dev_priv, CNL_PS_COEF_DATA_SET(pipe, id, set),
+				  tmp);
+	}
+
+	intel_de_write_fw(dev_priv, CNL_PS_COEF_INDEX_SET(pipe, id, set), 0);
+}
+
+inline u32 skl_scaler_get_filter_select(enum drm_scaling_filter filter, int set)
+{
+	if (filter == DRM_SCALING_FILTER_NEAREST_NEIGHBOR) {
+		return (PS_FILTER_PROGRAMMED |
+			PS_Y_VERT_FILTER_SELECT(set) |
+			PS_Y_HORZ_FILTER_SELECT(set) |
+			PS_UV_VERT_FILTER_SELECT(set) |
+			PS_UV_HORZ_FILTER_SELECT(set));
+	}
+
+	return PS_FILTER_MEDIUM;
+}
+
+void skl_scaler_setup_filter(struct drm_i915_private *dev_priv, enum pipe pipe,
+			     int id, int set, enum drm_scaling_filter filter)
+{
+	switch (filter) {
+	case DRM_SCALING_FILTER_DEFAULT:
+		break;
+	case DRM_SCALING_FILTER_NEAREST_NEIGHBOR:
+		cnl_program_nearest_filter_coefs(dev_priv, pipe, id, set);
+		break;
+	default:
+		MISSING_CASE(filter);
+	}
+}
+
 static void skl_pfit_enable(const struct intel_crtc_state *crtc_state)
 {
 	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);

drivers/gpu/drm/i915/display/intel_display.h

@@ -28,6 +28,7 @@
 #include <drm/drm_util.h>
 
 enum link_m_n_set;
+enum drm_scaling_filter;
 struct dpll;
 struct drm_connector;
 struct drm_device;
@@ -599,6 +600,9 @@ void intel_crtc_arm_fifo_underrun(struct intel_crtc *crtc,
 
 u16 skl_scaler_calc_phase(int sub, int scale, bool chroma_center);
 void skl_scaler_disable(const struct intel_crtc_state *old_crtc_state);
+u32 skl_scaler_get_filter_select(enum drm_scaling_filter filter, int set);
+void skl_scaler_setup_filter(struct drm_i915_private *dev_priv, enum pipe pipe,
+			     int id, int set, enum drm_scaling_filter filter);
 void ilk_pfit_disable(const struct intel_crtc_state *old_crtc_state);
 u32 glk_plane_color_ctl(const struct intel_crtc_state *crtc_state,
 			const struct intel_plane_state *plane_state);